1. Field of the Invention
The present invention relates to a rim-fitted tire with its weight unbalance corrected and a method of correcting a weight unbalance of a rim-fitted tire.
2. Description of the Related Art
It is well-known that vibrations occur if a rim-fitted tire with unbalanced weight is rotated. Such an unbalance acts as a couple of forces about a vertical axis parallel with the plane of rotation of the tire, and about a horizontal axis, respectively. The couple of forces acting about the horizontal axis is called static unbalance, while the couple of forces acting about the vertical axis is called dynamic unbalance.
That is, the static unbalance occurs when the center of gravity of the tire is not aligned with the rotating axis, while the dynamic unbalance occurs when there is a weight unbalance on both obverse and reverse surfaces of the tire, and an inertial axis passing through the center of gravity is not aligned with the rotating axis.
As a method of correcting such an unbalance, a method is known in which the static unbalance is first corrected, and then, the correction of the dynamic balance is separately made by rotating the tire and distributing balance weights. Nowadays, however, a method is mainly adopted in which the rim-fitted tire is mounted on a measuring instrument (balancer) and rotated to measure the amount of unbalance requiring correction, and one balance weight is fitted at one location on each of the observe and reverse rim flanges on the basis of that measurement, so as to simultaneously correct the static unbalance and the dynamic unbalance.
However, with this method of simultaneously correcting the weight unbalance, since the rim-fitted tire is rotated and measured on the axis of the balancer, there has been a drawback in that no consideration is given to a ground-contacting condition, i.e., the condition in which the rim-fitted tire is actually used. In addition, weight unbalance exhibits a certain distribution in the rim-fitted tire, and it is readily conceivable that the unbalance is not concentrated in one location. Nevertheless, at the time of making an actual correction of the balance, one balance weight is attached to each of the obverse and reverse sides of the rim (widthwise (axially) opposite ends of the rim) so as to correct the balance.
With this conventional method of correction, however, it cannot be said that a satisfactory correction can always be made since, as described above, it ignores the aspect that the tire rotates in contact with the ground.
More specifically, FIG. 1 schematically shows a rim-fitted tire which is rotated on the axis of a balancer, a balance weight "wa" being attached at a location a indicated by the balancer. In other words, the rim-fitted tire is overweight at a location b on the opposite side thereof.
When the rim-fitted tire is rotated in this state, its centrifugal force is balanced. When the tire is actually in contact with the ground, however, this balance does not hold.
FIG. 2 shows a state in which such a tire is actually mounted on a vehicle and is in contact with the ground.
That is, at points a and b located symmetrically about the center of the rim, an additional centrifugal force is created by the balance weight placed at the point a with the tire contacting the ground at the point b, so that vertical vibrations (moment acting in the direction of arrow A) and horizontal vibrations (moment acting in the direction of arrow B) occur in the tire.
To sum up, if the conventional balancing method is adopted, although vibrations can be controlled to a certain degree, a satisfactory remedy is not provided since the balance with respect to the tire contacting the ground is not taken into consideration.